|Publication number||US7221724 B2|
|Application number||US 10/268,022|
|Publication date||22 May 2007|
|Filing date||10 Oct 2002|
|Priority date||10 Oct 2002|
|Also published as||US20040071249|
|Publication number||10268022, 268022, US 7221724 B2, US 7221724B2, US-B2-7221724, US7221724 B2, US7221724B2|
|Original Assignee||Bitzmo, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Non-Patent Citations (5), Referenced by (8), Classifications (28), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The present invention relates to a precise timing generator in an integrated circuit. In particular, the present invention relates to a precise timing generator in an integrated circuit suitable for use with pulse position modulation (PPM) applications.
2. Discussion of the Related Art
Ultra wide bandwidth (UWB) communication is an emerging technology for high data rate wireless communication. In some proposed UWB systems, the signal comprises pulses of defined duration (e.g., Gaussian pulses) that can be transmitted with or without modulation of a conventional carrier. In addition, the UWB communication can occur over a wide frequency band, which may or may not be sub-divided into channels. These proposed UWB systems are disclosed, for example, in (a) U.S. Pat. No. 6,430,208, to Fullerton et al., Ser. No. 09/037,704, filed on Mar. 10, 1998, and (b) “Utra-Wide Bandwidth Time-Hopping Spread-Spectrum Impulse Radio for Wireless Multiple-Access Communications,” by M. Win et al., published in IEEE Transaction on Communication, Vol. 48, No. 4, April 2000, pp. 679–691.
In some of these proposed UWB systems, the pulses can be time-coded (“time-hopping”), pulse position or polarity modulated. Most of these proposed schemes require a precise timing generator to provide the precisely timed signals for transmission or reception. In the prior art, such as the system described in the U.S. Pat. No. 6,430,208 mentioned above, the timing generator circuit provided is large, occupying an integrated circuit separate from the signal processing integrated circuit, and dissipating a substantial amount of power (e.g., 500 mW). Thus, there is a need to provide a precise timing generator that is suitable for use in such application as UWB communications on the same integrated circuit as the signal processing circuit and which draws substantially less power than the precision timing generator of the prior art.
According to the present invention, a precision timing generator and an associate method provide a precise clock signal based on a reference clock signal. This precise clock signal can be used in any application in which a highly precise clock signal is required, such as for generating ultra-wide bandwidth (UWB) pulses using pulse-position modulation or time-hopping protocols. Since the precision clock signal under the present invention can be generated using analog CMOS circuit techniques, for signal processing applications, the precise clock signal can be generated on the same integrated circuit as the signal processing circuits and draws power that is substantially less than that drawn in the prior art for UWB applications.
According to one embodiment of the present invention, using the reference clock signal in a phase locked loop or delay locked loop, a number of clock signals of equal frequency are generated, each clock signal being separated from a consecutively following clock signal by a known phase. From these clock signals, two successive clock signals are selected for interpolation for higher precision according to a set of predetermined weights. The resulting interpolated clock signal has a phase offset that is intermediate between the selected clock signals, but in proportion to the predetermined weights. The weights can be expressed, for example, as binary fractions that sum to a binary ‘1’.
According to one embodiment of the present invention, the interpolator includes low pass filters that filter the selected clock signals, which are then amplified in variable gain amplifiers to provide signals that rise in proportion to their associated weights. These signals are then summed to provide a resulting clock signal. Such a clock signal has a precisely determined clock phase, and can be provided at approximately 50% duty cycle, such that it can also be used as a trigger signal for a triggered pulse generator.
In one implementation, a second interpolated clock signal is created by independently selecting and weighting a second group of clock signals. The two interpolated clock signals are then combined by a logic operation to provide a precise clock signal of a predetermined duty cycle and phase. As mentioned above, such a clock signal can be used as a trigger signal for a triggered pulse generator. Alternatively, such a clock signal can also be provided as an input signal to a pulse-shaping network, such as a passive filter. The pulse-shaping network may include passive elements (e.g., resistors, capacitors, inductors and diodes), an antenna, or any active element appropriate for the implementation.
The present invention is better understood upon consideration of the detailed description below and the accompanying drawings.
To facilitate comparison across the figures above, like elements in the above figures are provided like reference numerals.
The present invention can be implemented in an integrated circuit for communication over an ultra-wide bandwidth (UWB) wireless personal area network (WPAN).
As shown in
MAC circuit 102 includes digital logic interface 107, which interfaces with PHY circuit 101, and a microcontroller-based control system. The microcontroller-based control system includes microcontroller 108, which can be implemented by an embedded microprocessor (e.g., ARM), a run-time random access memory (RAM) 109 and non-volatile memory 110 (e.g., a flash memory). Software for microcontroller 108 can be stored, for instance, in non-volatile memory 110, and loaded into RAM 109 at run time.
Memory and I/O control circuit 103, which operates under the control of microcontroller 108, controls accesses to RAM 109, non-volatile memory 110, and external peripheral modules, or a host computer.
One implementation of precision timing generator 202 of
As shown in
Low pass filters 404 a and 404 b each receive one of the two selected clock signals output from selector 402 at terminals 306 a and 306 b, and integrate the corresponding voltage step at each rising or falling edge of each clock signal. The integrated voltage waveforms at terminals 411 a and 411 b, which correspond to integrating the voltage steps of the rising edges of clock signals 306 a and 306 b, respectively, are shown in
For use in a UWB communication application using pulse position modulation, design considerations relevant to the present invention include a trade-off between the resolution of coarse timing generator 302 and interpolator 303. For example, if each delay element of delay locked loop 401 is nominally 500 picoseconds (ps), then the nominally frequency of delay locked loop 401 would be 250 MHz, with neighboring clock signals being offset in phase by 500 ps. (Hence, the coarse timing resolution in coarse timing generator 302 is nominally 500 ps). If DAC 403 receives a 3-bit input, eight uniformly spaced output levels can be provided to control variable gain amplifiers 405 a and 405 b, thus providing eight fine-timing steps (62.5 ps each) within each 500 ps window. In a UWB application, coarse timing input can be modulated according to a code to achieve, for example, spectral spreading and multiple access control, while the fine timing input may be modulated according to a desired message stream (e.g., the information bits or payload to be transmitted). Thus, the resolution partitioning between the coarse and fine timing circuits may take into consideration both integrated circuit design trade-offs (e.g., current and area requirements) and communication design trade-offs (e.g., data rate, robustness to multipath propagation, accommodation of multiple access requirements, and noise immunity).
If it is desired to adjust the duty cycle of the resulting output waveform, two highly precise clock signals based on the same phase locked loop or delay locked loop can be obtained using two sets of clock signal selectors and interpolators. Such a circuit is illustrated by circuit 600 shown of
The above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting. Numerous modifications and variations within the scope of the present invention are possible. For example, the implementation of interpolator 303 shown in
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|U.S. Classification||375/355, 348/592, 327/270, 375/354, 342/450, 341/131, 327/231, 368/113, 327/105, 708/313, 342/357.27, 342/357.29|
|International Classification||H04L7/00, H03K5/15, H04B1/69, H03K5/13, H03L7/099, H04L7/033|
|Cooperative Classification||H04B1/7183, H03L7/0996, H03L7/0998, H03K5/133, H03K5/15013|
|European Classification||H04B1/7183, H03K5/13D, H03K5/15D, H03L7/099C2, H03L7/099C6|
|10 Oct 2002||AS||Assignment|
Owner name: BITZMO, INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SCHELL, STEPHAN;REEL/FRAME:013384/0453
Effective date: 20021007
|15 Aug 2008||AS||Assignment|
Owner name: ULTRABIT COMMUNICATIONS LLC, DELAWARE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BITZMO INC.;REEL/FRAME:021398/0088
Effective date: 20080610
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